The invention relates to a coating apparatus with a sputtering cathode which has an electrically conductive electrode connectable to a high-frequency generator on which an electrically nonconductive target defined by at least one straight edge is held by a solder bond and around which runs a dark space shield.
Coating apparatus of the above kind are now being manufactured and are generally known. Difficulties are encountered in such coating apparatus due to the solder bond between the electrode and the target on account of the greatly different expansion between the electrode and the target, for example when the target consists of aluminum oxide and the electrode of copper. Particularly in electrodes and targets of large area the target is often broken in such cases.
To prevent damage to the target, it is known to solder onto an electrode of large area a plurality of individual targets side by side like tiles on a wall, so as to avoid target breakage. It is disadvantageous in this case that this creates the danger of the evaporation of solder from between the individual targets, so that the coatings produced on the substrates are contaminated by the evaporated solder.
Instead of soldering a plurality of targets on a large-area electrode, it is also known in high-power coating apparatus to arrange two identical cathodes side by side, each with a target. In this case, however, it is a disadvantage that the sputtering rate decreases in the marginal areas of the targets. The result is that in both targets considerable residues of material remain due to marginal areas that are not or are incompletely evaporated. Furthermore, due to the two cathodes, the coating is irregular, especially when the substrates are situated precisely above the gap between the two cathodes.